1. Field of the Invention
This invention relates to an apparatus for forming pellets, or granules, from extruded strands of a thermoplastic material.
More specifically, this invention involves an improved rotary cutter apparatus cooperating with a die structure defining one or more melt extrusion orifices and adapted for operation while submerged in a cooling medium. The medium cools the thermoplastic material which usually is extruded through the orifices of the die in molten form.
2. Description of the Prior Art
It has been found, in working with conventional melt cutter devices, that the maintenance of the clearance between the knife and the die is very important and critical for proper cutting action. If this clearance becomes too large, for example as the result of excessive wear of the knife or variations in extrusion temperatures or pressures, poor and incomplete cutting action results and the quantity of fines produced generally increases. Pellets of thermoplastic polymers used in extrusion, injection molding, or blow molding processes are preferably desired to be free of fines, uniform in size, and with cleanly cut surfaces in order to enable them to be free flowing, and thereby avoid a possible variable volumetric feed to the injection, extrusion, or blow molding device.
Conversely, if the clearance between the knife and the die is reduced to zero, and if there is significant friction between them for example, as the result of bulging of the die face toward the knife, which may be caused by pressure of the molten thermoplastic against the die, severe wear of the knife as well as the die occurs. Scoring of the expensive die and knife breakage are also likely to occur.
Therefore, an object of this invention is the provision of an improved melt cutter apparatus for producing thermoplastic pellets or granules of uniform size and shape from thermoplastics. A particular object is the provision of a liquid phase melt cutter apparatus which will function effectively for long periods of time with a minimum amount of attention to the clearance between the knife and the die, a minimum production of fines, a minimum of knife breakage and wear, a minimum of die scoring and wear, and a minimum of adjustment or service during the operating life of the apparatus, particularly when starting up or shutting down the melt cutter apparatus.